Apparatus and method for well fluid sampling

ABSTRACT

A well fluid sampling tool ( 5 ) having a sample chamber ( 315 ) at least partly contained within an at least partially evacuated jacket ( 160, 165, 170 ), the outermost wall ( 160 ) of the jacket ( 160, 165, 170 ) being adjacent to or forming an outermost wall of the tool ( 5 ). In such a tool ( 5 ) the evacuated jacket ( 160, 165, 170 ) acts to maintain the sample as originally retrieved, e.g. in single phase form (at original temperature).

FIELD OF THE INVENTION

This invention relates to a well fluid sampling tool and to a well fluidsampling method.

The invention particularly, though not exclusively, relates to aso-called single phase or monophasic sampling tool, and related method.

BACKGROUND OF THE INVENTION

There are many circumstances where it is desirable to sample a fluidmaterial, whether as a gas, a liquid, or a mixture of the two, anddetermine its nature, for example, its physical and chemicalcomposition, to determine information about the body of fluid from whichthe sample was taken. On some such occasions the sample may be obtainedunder one set of ambient conditions—of pressure and temperature, say—andthereafter removed to a quite different set for analysis such that, ifunprotected, the sample's state—e.g. its physical and chemical form—maychange during this removal until it is no longer sufficientlyrepresentative of the original fluid. One typical example of thissituation occurs when sampling fluids issuing from geological formationsinto which a well, such as an oil/gas well, has been drilled. At thebottom of the well, which may be several miles deep, pressure andtemperature are high—possibly several hundred atmospheres, and in thelow hundreds of degrees Celsius. Whilst the formation fluid may underthese ambient conditions be a single phase fluid, nevertheless a sampleof this fluid transported to quite different ambient conditions of thesurface (specifically of pressure and temperature—often referred to asNAP, Normal Atmospheric Pressure, or as NTP, Normal Temperature andPressure), where it is to be analysed to reveal useful information aboutthe well, may easily separate into two or more distinct phases—forexample, a liquid phase, a gas phase (originally dissolved in theliquid), and a solid phase (originally suspended or in solution in theliquid).

As such, the separated sample is no longer truly representative of theoriginal fluid—or, at least, not in an easily-understood way—and so haslost much of its value. Indeed in some circumstances it may beimpractical to reconstitute the original fluid sampled.

Single phase sampling tools are known. For example, WO 91/12411(OILPHASE SAMPLING SERVICES) discloses a well is fluid sampling tool andmethod for retrieving single-phase hydrocarbon samples from deep wells.In that document the sampling tool is lowered to the required depth, aninternal sample chamber is opened to admit well fluid at a controlledrate, and the sample chamber is then automatically sealed. The wellfluid sample is subjected to a high pressure to keep the sample in itsoriginal single-phase form until it can be analysed. The sample ispressurised by a hydraulically-driven floating piston powered byhigh-pressure gas acting on another floating piston. Once sampling isinitiated e.g. by an internal clock, the entire sequence is automatic.

GB 2 252 296A (EXAL SAMPLING SERVICES) discloses an arrangement which ispressure compensated, so that as the container is lifted to the surface,and the ambient pressure and temperature drop, firstly the sample itselfis sealed off to prevent it expanding (and separating) under the reducedpressure, and secondly the original ambient pressure is positivelymaintained despite any temperature change seeking to cause acorresponding pressure change (so that temperature-induced pressure dropand phase separation is avoided). This end is attained by a samplerwherein the sample chamber, in which the sample itself is received andstored, is sealingly closed at one end by a moveable partition to theother side of which is applied either directly or indirectly (via abuffer fluid) a source of suitably pressured gas.

The aforementioned sampling tools essentially use compensationtechniques, i.e. the pressurised gases act on the sample to compensatefor pressure drop in the sample due to temperature drop. These samplingtools, therefore, require the provision of a gas reservoir andcomplicated mechanisms to apply pressure to the sample to compensate fortemperature reduction induced pressure changes.

SU 368 390 (MAMUNA et al) discloses a device for withdrawing samples offormation oil, including a body, a receiving chamber with a piston, andan inlet valve, wherein the receiving chamber is fitted with an electricheater connected to a thermometer mounted in the piston, with the aim ofpreserving the properties of the formation oil in the sample withdrawn.

WO96/12088 (OILPHASE SAMPLING SERVICES) discloses a well fluid samplingtool and method for retrieving reservoir fluid samples from deep wells.In this document the sampling tool is lowered to the required depth, aninternal sample chamber is opened to admit well fluid at a controlledrate, and the sample chamber is then automatically sealed. Thetemperature of the sampled well fluid is maintained at or near initialas sampled temperature to avoid the volumetric shrinkage otherwiseinduced by temperature reduction, mitigate precipitation of compoundsfrom the sample, and/or maintain the initial single phase condition ofthe sample. The sample chamber is thermally insulated, provided with astorage heater, electrically heated, given a high heat capacity, and/orpre-heated to sample temperature.

A problem with prior art single phase sampling tools is that the toolmust be lowered, in use, down within a is drillstring. The tool must,therefore, be of less than a predetermined outer diameter. However, thetool should also be as short as possible, for example, to seek to avoidthe tool becoming stuck or “hanging-up” within the drillstring.

It is an object of at least one aspect of the present invention toobviate or mitigate one or more of the aforementioned problems in theprior art.

It is a further object of at least one aspect of the present inventionto seek to provide an optimum sized sample chamber within a tool ofparticular outer dimensions (outer diameter and length).

SUMMARY OF THE INVENTION

These objects are addressed by the general solution of providing a wellfluid sampling tool with an evacuated chamber surrounding at least partof a sample chamber, an outer wall of the evacuated chamber beingadjacent to or preferably forming an outer wall of the tool.

According to a first aspect of the present invention there is provided awell fluid sampling tool having, at least in use, a sample chamber atleast partly contained within an at least partially evacuated jacket, anoutermost wall of the jacket being adjacent to or forming an outermostwall of the tool.

In such a tool the evacuated jacket acts to maintain the sample asoriginally retrieved, e.g. in single phase form (at originaltemperature).

Advantageously the sample chamber is substantially contained within theevacuated jacket.

Preferably, the evacuated jacket comprises first and second tubularbodies, the first tubular body comprising the outermost wall of thejacket and the second tubular body being provided within the firsttubular body, an evacuated chamber being provided between the twobodies.

Advantageously, the evacuated chamber is formed by a longitudinalannular space between the bodies.

The pressure in the annular space may be approximately between 10⁻⁷ PSIand 10⁻¹¹ PSI and typically around 10⁻⁸ PSI.

Preferably, the first and second bodies are formed in one piece, beingjoined at least one end.

Preferably also, the sample chamber is provided with a third tubularbody which is at least partly provided within the second tubular body.

Advantageously, sample temperature maintenance means are provided,preferably between the second and third tubular bodies.

Preferably, the temperature maintenance means include a plurality ofheaters spaced longitudinally between the second and third tubularbodies.

Advantageously the heaters are sized to seek to compensate for heat lossat their respective locations.

Advantageously first and second heaters provided at first and secondends of the third tubular body are more powerful than heaters provideddistal from the first and second ends. This arrangement is particularlyadvantageous so as to seek to compensate for heat loss from the ends ofthe sample chamber. Preferably the second heater is more powerful thanthe first heater.

Preferably the temperature maintenance means further comprises at leastone temperature sensor for detecting the temperature of the fluidsample.

Preferably the at least one temperature sensor measures the temperatureof an outer wall of the third tubular body.

Preferably the tool further comprises means for controlling admission ofa sample into the sample chamber.

The admission control means may comprise a floating piston controllablymoveable longitudinally within the sample chamber.

The admission control means may further comprise means for controllablymoving the floating piston.

The controllable movement means may comprise a further fluid and meansfor controllably reducing pressure of the further fluid.

Preferably the piston is mounted on and moveable along a piston rod.

The piston rod may have a piston stop at one end adapted to limit travelof the piston at that one end of the piston rod.

The piston rod may further carry a plug at another end. Advantageouslyends of the sample chamber are defined by he piston stop and the plug.

The tool may be provided with one or more sample inlet ports.

The tool may also be provided with one or more sample utlet ports, whichoutlet ports may be distinct from the inlet ports.

The tool may also provide means for removing a sample from the samplechamber.

The sample removal means may include first and second ports whichcommunicate with first and second outer ends of the sample chamber.Thus, in use, a pump may be connected across the first and second portsso as to apply a differential pressure across the first and second endsof the sample chamber, thereby effecting movement of the sample chamberwithin the tool towards one or more sample outlet ports.

In use, a sample transfer vessel may be connected to the one or moresample outlet ports via one or more valves so as to allow controllabletransfer of the sample from the sample chamber to the transfer vessel.

Advantageously the transfer vessel may include a further floating pistonprovided within a transfer chamber.

Preferably the transfer chamber is of substantially the same volume asthe sample chamber.

According to a second aspect of the present invention there is provideda well fluid sampling method comprising the steps of:

providing a well fluid sampling tool having a sample chamber at leastpartly contained within an evacuated jacket, an outermost wall of thejacket being adjacent to or forming an outermost wall of the tool;

lowering the tool down a wellbore to a location where well fluid is tobe sampled;

admitting a sample into the sample chamber by means of controllableadmission means;

sealing the sample chamber;

retrieving the sample to surface while substantially maintaining thetemperature of the sample;

removing the sample from the sample chamber into a chamber of a sampletransfer vessel.

By such a method it is sought to maintain the sample as originallysampled, e.g. in single phase form (and at substantially originaltemperature).

This may be achieved as the sample chamber has a predetermined volume;thus by seeking to maintain the temperature of the sample the pressureof the sample is also maintained.

Advantageously on admitting the sample into the sample chambertemperature and pressure outside the tool are measured and stored bysuitable measurement means and storage means.

According to a third aspect of the present invention there is provided awell fluid sampling tool including a sample chamber and an at leastpartially evacuated jacket surrounding at least part of the samplechamber, the evacuated jacket comprising first and second tubular bodieshaving an at least partially evacuated annular space therebetween, thefirst and second bodies being integrally formed with one another.

Preferably the first and second bodies are integrally connected to oneanother at least at or near first adjacent ends of each body.

Preferably such integral connection may be formed by welding, andadvantageously e-beam welding.

Preferably also, the first and second bodies are connected to oneanother at or near second adjacent ends of each body.

Advantageously a centraliser may be provided between the first andsecond bodies, which centraliser may preferably be made at least partlyfrom titanium.

According to a fourth aspect of the present invention there is provideda method of operating a well fluid sampling tool, the tool comprising asample chamber, heater means in thermal communication with the samplechamber and means for controlling the heater means including means formeasuring temperature external of the tool, the method comprising:

storing a preset temperature on the control means;

lowering the tool down a borehole;

continually monitoring the temperature external the tool atpredetermined intervals;

comparing the measured external temperature to the preset temperatureand if the measured external temperature is greater than the presettemperature then causing the heater means to heat at least part of thesample chamber to the measured external temperature.

Advantageously, as the tool is lowered if the external temperature isgreater than the preset temperature then the external temperature isstored as the preset temperature.

Advantageously as the tool is lowered the pressure external the tool isalso continually monitored, and preferably the highest external pressuremonitored is stored on the control means.

In a preferred embodiment the tool includes an electronic clock circuitand a memory logger circuit.

According to a fifth aspect of the present invention there is provided awell fluid sampling tool including a sample chamber and pressure reliefmeans communicating between the sample chamber and external the toolsuch that, in use, if pressure in the chamber exceeds a predeterminedlevel the pressure is relieved via the pressure relieve means.

The pressure relieve means may comprise a pressure relief valve or abreakable disc. The tool may include sample temperature maintenancemeans.

Provision of the pressure relief means seeks to avoid excessive pressurebuild-up within the sample chamber, e.g. due to thermal runaway of thetemperature maintenance means.

A tool according to any of the first, third or fifth aspectshereinbefore mentioned may be inserted into a borehole by wireline andmay be coupled together with similar tools or with other tools, forexample, memory pressure gauges, togging tools, spinners or the like, bythreaded cross-overs.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, which are:

FIGS. 1(A)-(E) a series of cross-sectional side views of a well fluidsampling tool according to an embodiment of the present invention in afirst position;

FIGS. 2(A)-(E) a series of cross-sectional side views of the well fluidsampling tool of FIGS. 1(A)-(E) in a second position;

FIGS. 3(A)-(E) a series of cross-sectional side views of the well fluidsampling tool of FIGS. 1(A)-(E) in a third position;

FIG. 4 a sectional view along line A—A of FIG. 2(B)

FIG. 5 a sectional view along line B—B of FIG. 2(B);

FIG. 6 a sectional view along line C—C of FIG. 2(B);

FIG. 7 a cross-sectional side view of a choke holder forming part of thetool of FIGS. 1(A)-(E).

FIG. 8 a sectional view along line D—D of FIG. 7;

FIG. 9 a sectional view along line E—E of FIG. 7;

FIG. 10 a sectional view along line F—F of FIG. 3(E);

FIG. 11(A) a schematic perspective view from one side to one end andabove of a plurality of heaters provided on a sample chamber comprisingpart of the tool of FIGS. 1(A)-(E);

FIG. 11(B) a schematic perspective view from one side to one end andalso to an enlarged scale of one of the heaters of FIG. 11(A) providedon the sample chamber comprising part of the tool of FIGS. 1(A)-(E);

FIG. 12 a schematic diagram of electronic circuitry associated with thetool of FIGS. 1(A)-(E);

FIGS. 13(A)-(C) a series of detailed circuit diagram of a clock boardcomprising part of the electronic circuitry of FIG. 12;

FIGS. 14(A)-(C) a series of detailed circuit diagram of a logger boardcomprising part of the electronic circuitry of FIG. 12;

FIG. 15 a detailed circuit diagram of a heater electronics boardcomprising part of the electronic circuitry of FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIGS. 1(A)-(E) there is illustrated a well fluidsampling tool, generally designated 5, according to an embodiment of thepresent invention. The tool 5 has a first end 10, which end is normallythe uppermost end when the tool 5 is conveyed down a borehole of a well,and a second end 15, which end is normally the lowermost end when thetool 5 is conveyed down the borehole.

The preferred maximum outer diameter of the tool 5 is approximately 2″so as to facilitate ease of transit of the tool 5 through an innerboreof a standard 2¼ test valve (not shown) up and down.

The tool 5 comprises a connector in the form of a top cross-over 20 bymeans of which the tool 5 can be connected to wireline, slickline,electric line or the like so as to be conveyed down or up a borehole ofa well. Indeed the tool 5 may be coupled together with similar tools orwith other downhole tools as is known in the art, e.g. by threadedcross-overs.

An end of the top cross-over 20 is threadably connected to and sealablyengaged with a first end of a battery housing 25, which housing 25provides a battery chamber holding a battery 30. In this embodiment thebattery 30 is a lithium battery. The battery 30 powers allelectrical/electronic components of the tool 5 hereinafter described.

A second end of the battery housing 25 is threadably connected to andsealably engaged with a first end of a clock board housing 35. The clockboard housing 35 provides a clock board chamber 40, which chamber 40holds a clock board 45 and a solenoid valve 50 which is controlled bythe clock board 45.

A second end of the clock board housing 35 is threadably connected toand sealably engaged with a first end of a solenoid nipple 55.

A second end of the solenoid nipple 55 is threadably connected to andsealably engaged with a first end of a buffer chamber housing 60. Thebuffer chamber housing 60 provides a buffer chamber 65 which when thetool 5 is initially run downhole, prior to sampling, is filled with air.Further an input port 70 of the solenoid nipple 55 at the second end ofthe solenoid nipple 55 which communicates with the solenoid valve 50 vialine 56 through the nipple 55 is connected to a first end of a tubingpiece 75. The tubing piece 75 is filled with an hydraulic fluid, e.g. amineral oil.

A second end of the buffer chamber housing 60 is threadably connected toand sealably engaged with a first end of a buffer chamber bleed-offnipple housing/prime port sub 80. The buffer chamber bleed-off nipplehousing/prime port sub 80 provides a first output port 85 which isconnected to a second end of the tubing piece 75, a first input port 90at a second end of the buffer chamber bleed-off nipple housing 80 whichcommunicates with the first output port 85 via a choke 86 including apressure multiplier 91 which multiplier 91 divides (reduces) fluidpressure seen at the first input port 90 by, for example, X15 to providea lower pressure at the first output port 85. Thus if fluid pressure atthe first inlet port 90 is 15,000 PSI, fluid pressure at the firstoutlet port 85 would be 1,000 PSI. The choke 86 further provides apressure activated valve/flow regulator 101.

In this way the pressure of fluid across the first inlet port 90 to thefirst outlet port 85 is divided by the multiplier 91, while the flowrate of fluid flowing from the first inlet port 90 to the first outletport 85 is controlled. This control is important in controlling thetiming of sample acquisition as will hereinafter become apparent. It is,for example, important not to sample too quickly thereby causing phaseseparation.

The housing/sub 80 also houses a pressure and temperature transducer 81which measures the ambient downhole pressure and temperature before, at,and after the time of sampling and sends such information to a loggerboard 114 or alternatively the clock board 45 or a heater electronicsboard 115.

The second end of the housing/sub 80 is threadably connected to andsealably engaged with a first end of a heater board housing 105. Theheater board housing 105 provides an air filled chamber 110 whichcontains the logger board 114 and a heater electronics board 115.

A second end of the heater board housing 105 is threadably connected toand sealably engaged with a first end of a connector piece 120. Thefirst end of the connector piece 120 provides a first output port 125which is connected to the first input port 90 of the housing/sub 80 viaa first pipe piece 130.

A second end of the connector piece 120 is provided with a first inletport 140 which communicates with the first outlet port 125.

A second end of the connector piece 120 is rigidly connected to a firstend of a first tubular body 160. The first tubular body 160 comprises anoutermost wall of the tool 5. The first tubular body 160 is integrallyformed at or near a second end thereof with a second tubular body 165such that the first and second tubular bodies 160, 165 are substantiallyconcentric and an annular space 170 is formed between the two bodies160, 165. The annular space 170 is at least partially evacuated, e.g. toa pressure of around between 10⁻⁷ PSI and 10⁻¹¹ PSI, and typicallyaround 10⁻⁸ PSI.

The annular space 170 is sealed at or near the first end of the firsttubular body 160 by a portion 161 of connector piece 120, which portion161 may be welded to the first tubular body 160, e.g. by e-beam welding.Further a centraliser 175 is provided between the first and secondtubular bodies 160,165.

The first and second tubular bodies 160, 165 and the evacuated annularspace 170, therefore, form an evacuated jacket, wherein an outermostwall of the jacket comprises an outermost wall of the tool 5.

Contained substantially concentrically within the second tubular body165 is a third tubular body 180. The third tubular body 180 is sealed ata first end by an end plug 185 which has a through flow orifice 190allowing communication between an hydraulic chamber 195 of the thirdtubular body 180 and the first input port 140. The hydraulic chamber 195is initially filled with hydraulic fluid, e.g. mineral oil.

As can be seen from FIGS. 1(D) and 1(E) a further annular space 200 isprovided between the second and third tubular bodies 165, 180. Aplurality of heaters 205 are provided in the annular space 200.Referring to FIGS. 11(A) and (B) there is illustrated in more detail theheaters 205 provided upon an outer surface of the third tubular body180. As can be seen, in this embodiment eight heaters are provided alongthe length of the third tubular body 180. The heaters 205 provided ateach end of the third tubular body 180 are more powerful—i.e. capable ofdissipating a larger amount of heat—than the other heaters. This isbecause heat loss can be expected to be greater from the ends of thethird tubular body 180, in use.

As can further be seen from FIG. 11 a plurality of pressure/temperaturetransducers (PRT's) 210 are provided on the outer surface of the thirdtubular body 180. In use, the PRT's 210 detect the pressure and/ortemperature of a sample contained within the third tubular body 180. Themeasured pressure/temperature is compared to the originally sampledpressure/temperature stored by the heater electronics board 105, and ifthe measured pressure/temperature is below the originally sampledpressure/temperature the board 105 switches on the heaters 205 until theoriginally sampled pressure/temperature is regained.

A second end of the first tubular body 160 is threadably connected toand sealably engaged with a portion of the third tubular body 180adjacent a second end thereof. The second end of the third tubular bodyprovides a plurality of sample ports 211 through a side wall thereof. Inthis embodiment there are four such sample ports 211. In use, two sampleports 211 are used for retrieving a sample into the tool 5, while theother two sample ports 211 are used for retrieving the sample out of thetool 5. Thus when retrieving the sample into the tool 5 the first twosample ports 211 are open and the second two sample ports 211 areplugged by appropriate means, while when retrieving the sample out ofthe tool 5 the first two sample ports 211 are appropriately plugged,while the second two sample ports are unplugged. This arrangement seeksto ensure that foreign matter such as dirt is not entrained into thesample.

The second end of the third tubular body 180 is threadably connected toand sealably engaged with a dog housing 215. The dog housing 215includes a tapered recess 220 for reception of spring-loaded dogs 225carried by a sampling assembly 230 moveable longitudinally within thethird tubular body 180 and dog housing 215.

The sampling assembly 230 comprises a floating piston 235, a firstsurface of which is exposed to the pressurised hydraulic fluid. Thepiston 235 is mounted for longitudinal movement upon a piston rod 240.The piston rod 240 provides a piston stop 245 at a first end thereof.Further the sampling assembly provides at a second end of the piston rod240 an end valve plug 244 which carries an end valve body 250. The endvalve body 250 carries the spring-loaded dogs 225. It is noted that thefloating piston 235, the end valve plug 245 and the end valve body 250all carry on their outer surfaces one or more seals so as to providesealing engagement with an internal surface of the third tubular body180 and/or an internal surface of the dog housing 215 as the samplingassembly 230 is held within and moves within the third tubular body 180and the dog housing 215.

The recess 220 communicates with an outer surface of the dog housing 215via through-apertures 254 each containing a grub screw 255 and filterscreen 260. In use, a tool (not shown) can be applied to the dogs 225via the apertures 254 to effect collapse of the dogs 225, as will bedescribed hereinafter.

The valve end body 250 further provides a pressure relief means 265(which may preferably be in the form of a burst disc or alternatively apressure relief valve) and nipple 270 protruding from an end thereof.The pressure relief means 265 may be designed so as to relieve pressureof a sample within the tool 5 if the pressure exceeds a predeterminedvalue.

For retrieval of a sample into the tool 5, a second end of the doghousing 215 is threadably connected to and sealably engaged with a firstend of a nose cone 275 or cross-over to another tool. The nose cone 275includes a plurality of inlet ports 280 (in this embodiment four) at asecond end thereof.

Protruding from the second end of the dog housing 215 and carriedthereby is a front inlet plug 285 having a through flow orifice 290capable of receiving the nipple 270. The nipple 270 carries one or moreseals 295 such that the nipple 270 may be sealably engaged in theorifice 290.

For retrieval of a sample from the tool 5 the nose cone 275 is replacedby a transfer head 300. The dog housing 215 is threadably connected toand sealably engaged with a first end of the transfer head 300. A secondend of the transfer head 300 provides a pump connection port 305. As canbe seen from FIG. 3C the housing/sub 80 provides a further pumpconnection port 310. As will be described hereinafter, in use, a pump(not shown) may be connected across the pump connection ports 305, 310to effect removal of a sample. Alternatively the housing/sub 80 may beremoved while maintaining pressure of the sample.

As will be appreciated from the foregoing, in use, a sample chamber 315is formed by a second face of the floating piston 235, inner wall of thethird tubular body 180, and an end of the end valve plug 245. In thisembodiment the volume of the sample chamber 315 is approximately 300 cc.However, it is envisaged that in alternative embodiments the chamber 315volume may be in the range 300 cc-600 cc and preferably 350 cc-500 cc.

Regarding material selection, the first and second tubular bodies 160,165 may each be made from stainless steel. In this embodiment the firsttubular body 160 is designed to withstand a pressure of approximately20,000 PSI from outwith. Further the third tubular body 180 may be madefrom stainless incanel, and designed to withstand a pressure ofapproximately 15,000 to 20,000 PSI from within.

Referring now to FIG. 12 there is shown a schematic diagram ofelectronic circuitry associated with the tool 5. The electroniccircuitry comprises the battery 30 which powers the clock board 45,logger board 114 and heater electronics board 115. As can be seen fromFIG. 12 the clock board 45 is connected to and controls solenoid valve50. Further the clock board 45 is connected to the logger board 114 suchthat at a predetermined (programmable) time a clock on the clock board45 activates the solenoid valve 50, causing the pressure and temperaturetransducer 81 to instantaneously measure the downhole pressure andtemperature and log these measurements to the clock board 45. The clockboard 45 is further connected to the heater electronics board 115 suchthat the measured value of temperature and pressure at time of samplingstored in a memory on the clock board 45 can be compared to the measuredvalues of temperature measured by the temperature transducers 210 whilethe tool 5 is retrieved to surface, and indeed thereafter until thesample is removed from the tool 5, in order that the heater electronicsboard 115 can thereby seek to maintain the original sampled conditionswithin the sample chamber 315 by means of the heaters 205.

Referring now to FIGS. 13(A) through 15, which show circuit diagrams forvarious parts of the electronic circuitry of FIG. 12. It will beappreciated that each of these FIGS. 13(A)-15, includes traditionalcircuit diagram numbering and symbols in addition to the specificreference numerals referenced in this specification. Such symbols andnumbering are known in the art. However, in general, the symbols andnumbering may be identified as follows: the reference symbols R# (where# is a number) refer to resistors; the reference symbols C# (where # isa number) refer to capacitors, the reference symbols U3* (where * is aletter) refer to inverters; the reference symbols U4* (where * is aletter) refer to NAND gates, the reference symbols Q# (where # is anumber) refer to transistors, and the reference symbols D# (where # is anumber) refer to diodes.

Referring to FIGS. 13(A)-(C), the clock board 45 comprises a regulator320 for powering the clock board 45, an analog-to-digital convertor 325,a memory 330, a microprocessor 335 and a solenoid control circuit 340.The clock board 45 includes a communications line Rx1 which allowscommunication to and from a computer before and after sampling, solenoidcontrol lines S1 and S2 and communications line SWC to logger board 114.

Referring to FIGS. 14(A)-(C), the logger board 114 comprises a regulator345, a communications receive/decode circuit 350, an analog-to-digitalconvertor 355, a microprocessor 360, a sampling pressure/temperaturememory 365, addressing latches 370, and a flash memory for data storage375. The logger board 114 also provides temperature input lines T4, T5and pressure input lines T6, T7, T8, and T9 from thetemperature/pressure transducer 81, as well as communication output lineT12 which may be connected to a computer after retrieval of the tool 5from downhole.

Referring now to FIG. 15 there is show circuitry of the heaterelectronics board 115 which comprises a heater control circuit 380having an output T14, CH4, T15, CH5, T16, CH6 to each of the heaters205, an input VBATT from the battery 30 and inputs Q3, Q5, and Q7 fromthe latches 370 of the logger board 114.

The heater electronics board 115 also provides input circuit 385comprising inputs T1, T2, and T3 from the temperature transducers 210and outputs CH0, CH1, and CH2 to the analog-to-digital converter 355 ofthe logger board 114.

In use, prior to the tool 5 being lowered down a borehole the clock onthe clock board 45 is set to activate the solenoid valve 50 after apredetermined time.

The tool 5 is then lowered down within a borehole, e.g. by wireline, ina first position as illustrated in FIGS. 1(A)-(E). In this firstposition pressurised hydraulic fluid, e.g. mineral oil, is containedwithin the hydraulic chamber 195. The pressurised fluid holds thefloating piston 235 at the second end of the piston rod 240 against theend valve plug 245. In this position a first two of the sample ports 211are appropriately plugged, while a second two of the sample ports 211are left opened. However, well fluid cannot enter into the tool 5 viathose ports 211 as the force of the pressurised hydraulic fluid actingon the piston 235 exceeds the force of the well fluid seeking to enterthe tool 5.

It should be noted that the heaters 205 may be used to heat thehydraulic fluid within the third tubular body 80. Such heating may occuron surface, while the tool 5 is lowered down the borehole, and/or whenthe tool 5 is lowered to a required position. In this way the thirdtubular body 180 may be pre-heated to close to an expected sampletemperature, thereby seeking to avoid cooling of a sample when it entersthe sample chamber 315.

After the predetermined time the clock activates the solenoid valve 50.This causes a flow path to open between the tubing piece 75 and bufferchamber 65 thereby allowing mineral oil to bleed into the buffer chamber65. This causes hydraulic fluid, i.e. mineral oil, to exit the hydraulicchamber 195 and bleed into the buffer chamber 65 via first pipe piece130, choke 86 and tubing piece 75. Thus the pressure of the hydraulicfluid is eventually caused to fall below the ambient downhole pressure.At this point the piston 235 begins to move towards the piston stop 245thereby admitting sample into the sample chamber 315.

As sample enters the sample chamber 315 the piston 235 moves towards andultimately strikes the piston stop 245. It is noted that a first end ofthe nipple 270 is attached to an end of the end valve plug 244. Thus theeffective area of the first (top) end of the end valve plug 244 isgreater than the effective area of the second (bottom) end of the endvalve plug 244. That is to say the effective well fluid pressure seen atthe first end is less than that seen at the second end. Thus, a pressureimbalance exists causing the sampling assembly 230 to move towards thefirst end of the third tubular body 180. Such movement causes the samplechamber 315 to be sealed from the ports 211. Continued movement causesthe dogs 225 to engage in recess 220. In this way a well fluid sample isretrieved into the sample chamber 315. The tool 5 is then in theposition shown in FIGS. 2(A)-(E).

The tool 5 may then be retrieved to the surface, and the sampleretrieved out of the tool 5 as hereinafter described. However, beforethe sample is retrieved out of the tool the temperature and pressure ofthe sample within the fixed volume sample chamber 315 is monitored bytemperature transducers 210, compared to the original values detected bytransducer 310 stored on the clock board 45, and if the temperature ofthe sample falls below the originally sampled values the logger board114 circuitry causes the heater controller circuit 380 to controllablyturn on the heaters 205 until the original values are regained. In thisway the. tool 5 seeks to maintain the sample in its original state. Theevacuated jacket forming an outer wall of the tool 5 assists inmaintaining the sample in its original state by seeking to reduce heatloss therefrom.

Referring finally to FIGS. 3(A)-(E) once the tool 5 is retrieved thesample may be retrieved from the tool 5 by the following procedure,either on-shore e.g. in a laboratory, or alternatively off-shore, iffacilities permit. Firstly, the nose cone 275 is replaced by a transferhead 300. Secondly, the first two sample ports 211 are plugged, and thesecond two sample ports 211 unplugged and connected to a transfer vesselvia an on-off valve. Thirdly, the clock board 45 is interrogated todeduce the as-sampled temperature and pressure values. Fourthly, a pump(not shown) is connected across the pump connection ports 305, 310 andthe pressure thereacross equalised with the pressure of the sample.Fifthly, a tool (not shown) may be applied to collapse the dogs 225. Thesample 315 is then free to move within the tool 5.

Next a pressure imbalance is provided between the pump connection ports305, 310 thereby causing the sample and the sampling assembly 230 tomove towards the second two sample ports 211. Samples can thencommunicate with these ports 211. Finally, the on-off valve is openedand sample transferred into the transfer vessel by manipulation of thepressure imbalance while carefully maintaining the volume of the sampleat all times, and also seeking to maintain the temperature and pressureof the sample as originally taken from the well.

It will be appreciated that the embodiment of the invention hereinbeforedescribed is given by way of example only, and is not meant to limit thescope of the invention in any way.

What is claimed is:
 1. A well fluid sampling tool comprising a samplechamber at least partly surrounded by an at least partially evacuatedjacket and a separate annular space, the sample chamber and separateannular space being separated by a tubular member, wherein the annularspace is at least partly surrounded by the at least partially evacuatedjacket, an outermost wall of the jacket being adjacent to or forming anoutermost wall of the tool.
 2. A well fluid sampling tool as claimed inclaim 1, wherein the sample chamber is substantially surrounded by theevacuated jacket.
 3. A well fluid sampling tool as claimed in claim 1,further comprising sample temperature maintenance means.
 4. A well fluidsampling tool as claimed in claim 3, wherein the temperature maintenancemeans further comprises at least one temperature sensor for detectingthe temperature of the fluid sample.
 5. A well fluid sampling tool asclaimed in claim 1, wherein the tool further comprises means forcontrolling admission of a sample into the sample chamber.
 6. A wellfluid sampling tool as claimed in claim 5, wherein the admission controlmeans comprises a floating piston controllably moveable longitudinallywithin the sample chamber.
 7. A well fluid sampling tool as claimed inclaim 6, wherein the admission control means furthers comprise means forcontrollably moving the floating piston.
 8. A well fluid sampling toolas claimed in claim 7, wherein the controllable movement means comprisesa fluid and means for controllably reducing pressure of said fluid.
 9. Awell fluid sampling tool as claimed in claim 6, wherein the piston ismounted on and moveable along a piston rod.
 10. A well fluid samplingtool as claimed in claim 9, wherein the piston rod has a piston stop atone end adapted to limit travel of the piston at that one end of thepiston rod.
 11. A well fluid sampling tool as claimed in claim 10,wherein the piston rod further carries a plug at another end.
 12. A wellfluid sampling tool as claimed in claim 11, wherein ends of the samplechamber are defined by the piston stop and the plug.
 13. A well fluidsampling tool as claimed in claim 1, wherein the tool further comprisesat least one or more sample inlet port.
 14. A well fluid sampling toolas claimed in claim 13, wherein the tool further comprises at least onesample outlet port.
 15. A well fluid sampling tool as claimed in claim1, wherein the tool further comprises means for removing a sample fromthe sample chamber.
 16. A well fluid sampling tool as claimed in claim15, wherein the sample removal means includes first and second portswhich communicate with first and second outer ends of the samplechamber.
 17. A well fluid sampling tool as claimed in claim 15, furthercomprising first and second ports disposed such that, when a pump isconnected across the first and second ports, a differential pressure isapplied across first and second ends of the sample chamber, therebyeffecting movement of the sample within the tool towards at least onesample outlet port.
 18. A method of operating a well fluid sampling toolaccording to claim 1, the tool further comprising heater means inthermal communication with the sample chamber and means for controllingthe heater means including means for measuring temperature external ofthe tool, the method comprising: storing a preset temperature on thecontrol means; lowering the tool down a borehole; continually monitoringthe temperature external the tool at predetermined intervals; comparingthe measured external temperatures to the preset temperature and if themeasured external temperature is greater than the preset temperaturethen causing the heater means to heat at least part of the samplechamber to the measured external temperature.
 19. A method as claimed inclaim 18, comprising the further step of continually monitoring thepressure external the tool.
 20. A method as claimed in claim 19,comprising the further step of storing the highest external pressuremonitored on the control means.
 21. A method as claimed in claim 18,comprising the further step of providing the tool with an electronicclock circuit and a memory logger circuit.
 22. A method of operating awell fluid sampling tool according to claim 1, the tool furthercomprising heater means in thermal communication with the sample chamberand means for controlling the heater means including means for measuringtemperature external of the tool, the method comprising: storing apreset temperature on the control means; lowering the tool down aborehole; continually monitoring the temperature external the tool atpredetermined intervals; comparing the measured external temperatures tothe preset temperature and if the measured external temperature isgreater than the preset temperature then causing the heater means toheat at least part of the sample chamber to the measured externaltemperature; and as the tool is lowered, determining if the externaltemperature is greater than the preset temperature and, if so, storingthe external temperature as the preset temperature.
 23. A well fluidsampling tool comprising a sample chamber at least partly surrounded byan at least partially evacuated jacket and a separate annular space, thesample chamber and separate annular space being separated by a tubularmember, wherein the annular space is at least partly surrounded by theat least partially evacuated jacket, an outermost wall of the jacketbeing adjacent to or forming an outermost wall of the tool, wherein theevacuated jacket comprises first and second tubular bodies, the firsttubular body comprising the outermost wall of the jacket and the secondtubular body being disposed within the first tubular body, an evacuatedchamber being disposed between the two bodies.
 24. A well fluid samplingtool as claimed in claim 23, wherein the evacuated chamber is formed bya longitudinal annular space between the bodies.
 25. A well fluidsampling tool as claimed in claim 24, wherein the pressure in theannular space is between approximately 10⁻⁷ PSI and 10⁻¹¹ PSI.
 26. Awell fluid sampling tool as claimed in claim 25, wherein the pressure inthe annular space is around 10⁻⁸ PSI.
 27. A well fluid sampling tool asclaimed in claim 23, wherein the first and second tubular bodies areformed in one piece, being joined at at least one end.
 28. A well fluidsampling tool as claimed in claim 27, wherein the first and secondtubular bodies are integrally connected to one another proximaterespective first adjacent ends of each body.
 29. A well fluid samplingtool as claimed in claim 28, further comprising an integral connectionformed by welding.
 30. A well fluid sampling tool as claimed in claim29, wherein the integral connection is formed by e-beam welding.
 31. Awell fluid sampling tool as claimed in claim 23, wherein the samplechamber is disposed within a third tubular body which is at least partlydisposed within the second tubular body, said annular space beingdefined between the third and second tubular bodies, wherein said thirdtubular body is the tubular member.
 32. A well fluid sampling tool asclaimed in claim 23, further comprising a third tubular body at leastpartially disposed within the second tubular body, and sampletemperature maintenance means being disposed between the second andthird tubular bodies.
 33. A well fluid sampling tool as claimed in claim32, wherein the temperature maintenance means include a plurality ofheaters spaced longitudinally between the second and third tubularbodies.
 34. A well fluid sampling tool as claimed in claim 33, whereinthe plurality of heaters compensate for heat loss at their respectivelocations.
 35. A well fluid sampling tool as claimed in claim 33,further comprising first and second heaters disposed at first and secondends of the third tubular body respectively which are more powerful thaneach of the heaters of the plurality of heaters.
 36. A well fluidsampling tool as claimed in claim 35, wherein the second heater is morepowerful than the first heater.
 37. A well fluid sampling tool asclaimed in claim 23, wherein the first and second tubular bodies areconnected to one another proximate respective second adjacent ends ofeach body.
 38. A well fluid sampling tool as claimed in claim 23,further comprising a centraliser disposed between the first and secondbodies.
 39. A well fluid sampling tool as claimed in claim 38, whereinthe centraliser is made at least partly from titanium.
 40. A well fluidsampling tool as claimed in claim 23, wherein the tool further comprisespressure relief means communicating between the sample chamber andexternal the tool such that, in use, if pressure in the chamber exceedsa predetermined level the pressure is relieved via the pressure reliefmeans.
 41. A well fluid sampling tool as claimed in claim 40, whereinthe pressure relief means comprise a pressure relief valve or abreakable disc.
 42. A well fluid sampling tool comprising a samplechamber at least partly surrounded by an at least partially evacuatedjacket and a separate annular space, the sample chamber and separateannular space being separated by a tubular member, wherein the annularspace is at least partly surrounded by the at least partially evacuatedjacket, an outermost wall of the jacket being adjacent to or forming anoutermost wall of the tool, wherein the temperature maintenance meansfurther comprises at least one temperature sensor for detecting thetemperature of the fluid sample, and wherein the at least onetemperature sensor measures the temperature of an outer wall of thethird tubular body.
 43. A well fluid sampling method comprising thesteps of: providing a well fluid sampling tool having a sample chamberat least partly surrounded by an evacuated jacket and a separate annularspace, the sample chamber and separate annular space being separated bya tubular member wherein the annular space is at least partly surroundedby the at least partially evacuated jacket, an outermost wall of thejacket being an outermost wall of the tool; lowering the tool down awellbore to a location where well fluid is to be sampled; admitting asample into the sample chamber by means of controllable admission means;sealing the sample chamber; retrieving the sample to surface whilesubstantially maintaining the temperature of the sample; removing thesample from the sample chamber into a chamber of a sample transfervessel.
 44. A method as claimed in claim 43, wherein the sample chamberhas a predetermined volume.
 45. A method as claimed in claim 43,comprising the further steps of, on admitting the sample into the samplechamber, measuring and storing temperature and pressure outside thetool.
 46. A method of operating a well fluid sampling tool, the toolcomprising a sample chamber, heater means in thermal communication withthe sample chamber and means for controlling the heater means includingmeans for measuring temperature external of the tool, the methodcomprising: storing a preset temperature on the control means; loweringthe tool down a borehole; continually monitoring the temperatureexternal the tool at predetermined intervals; comparing the measuredexternal temperatures to the preset temperature and if the measuredexternal temperature is greater than the preset temperature then causingthe heater means to heat at least part of the sample chamber to themeasured external temperature; wherein the method further comprises thestep of, as the tool is lowered determining if the external temperatureis greater than the preset temperature and, if so, storing the externaltemperature as the preset temperature.